Since the discovery of 2(2-hydroxyphenyl)2H-benzotriazoles as effective ultraviolet light absorbers and ultraviolet stabilizers, especially in plastic materials, much attention has been paid to the synthesis of novel and unusual 2(2-hydroxyphenyl)2H-benzotriazole derivatives.
More recently, attention has shifted to less volatile, more compatible and ultimately polymerizable, polymeric and polymer bound ultraviolet stabilizers of the 2(2-hydroxyphenyl)2H-benzotriazole (2HB) category. Initial photophysical studies showed these compounds to be effective ultraviolet stabilizers. There are also some indications that some of these compounds may also act as quenchers of the excited states.
Before the use of the 2(2-hydroxyphenyl)2H-benzotriazoles (2HB's), ultraviolet stabilizers of the category of 2-hydroxybenzophenones were, and still are, used extensively, but few polymerizable 2-hydroxybenzophenone ultraviolet stabilizers are now available commercially. Such compounds are typified in U.S. Pat. Nos. 2,938,883 to Raisch and 2,947,723 to Clark.
Although much synthetic work has been done on the synthesis of 2(2-hydroxyphenyl)2H-benzotriazole (2HB's) some years ago, no attempts were made to combine the 2(2-hydroxyphenyl)2H-benzotriazole and the 2-hydroxybenzophenone chromophor in one molecule. It has been found that more than one benzotriazole unit may be easily introduced in one molecule when highly activated. Multi-hydroxylated phenyl compounds such as resorcinol or phloroglucinol have been used to produce a new series of compounds with interesting ultraviolet absorbing properties.